This invention relates generally to refining apparatus. More particularly, the present invention relates to refining apparatus having a rotor and a stator forming a cylindrical or conical refining gap between rotor and stator.
Nowadays most of the refiners built are of twin disc or conical design. The disadvantages of the twin disc refiner are the changing relative speed along the length of the refining zone, a relatively high idle running rating and problems with centering the rotor, particularly at low throughputs. A significant disadvantage of the conical refiner known is the poor pumping effect. This leads to throughput difficulties and, as a result, the need to enlarge the grooves in the refining zone, which reduces the edge length. Possible other disadvantages are the relative displacement of the knives when being set in relation to one another, the need for a sturdy design as a result of the bearing forces occurring, and the difficulties in changing the refiner plates, which lead to high manufacturing costs. With a cylindrical refiner, as known from U.S. Pat. No. 5,813,618, for example, many of these disadvantages can be avoided, however there may be problems with the throughput, similar to those occurring with the conical refiner.
The aim of the invention is, therefore, to circumvent the disadvantages of the cylindrical and conical refiners known, in order to also permit higher throughputs.
The invention is thus characterized by the pulp feed channel extending in radial direction from the inlet pipe up to the refining gap. The pulp fed in is accelerated here by the rotating movement of the rotor in circumferential direction, which causes a pressure increase in the liquid. On the one hand, this pressure build-up eliminates the need for a feed pump and on the other, it provides good rotationally symmetrical inflow.
An advantageous configuration of the invention is characterized by the pulp feed channel having a rotationally symmetrical design. This results in even and rotationally symmetrical inflow to the refining flaps.
An advantageous further development of the invention is characterized by the inlet pipe connected to the pulp feed channel being on an axis which coincides with the axis of the rotor. In this way the pulp is fed directly into the axis of the refiner, which causes the pulp to be accelerated partially in the pipe before entering the pulp feed channel on the one hand and provides even more uniform pulp distribution on the other hand.
A favorable farther development of the invention is characterized by a disc being provided between the inlet pipe and the refining gap which limits the pulp feed channel. If the pulp is fed in outside the axis, the disc deflects the pulp at the shaft and directs it in rotational symmetry outwards, where the liquid is accelerated radially outwards between disc and front face of the rotor and subsequently flows evenly distributed into the refining gap.
A favorable configuration of the invention is characterized by a cylindrical rotor being provided. The rotor can also be conical, widening in the flow direction of the pulp or, as an alternative, a conical rotor narrowing in the flow direction of the pulp. Thus, the shape of refining gap suitable for the given requirements can be used.
An advantageous further development of the invention is characterized by a twin rotor being provided. With a twin rotor, where the rotor can be cylindrical as well as conical (widening cone or narrowing cone), it is possible to achieve a high throughput, also with even inflow to the refining gaps in rotational symmetry.
A favorable further development of the invention is characterized by the pulp feed channel being located between the two rotors. In particular, if an inlet pipe positioned in the axis of a rotor is used, the pulp can be fed into the center of the refiner and then directed outwards by the rotating movement, which leads to a corresponding rise in pressure. Further downstream the pulp is fed into the center of the corresponding refining gap, which achieves further evening out of the pulp feed.
An advantageous configuration of the invention is characterized by a cylindrical and a conical refining gap being arranged in series. This arrangement of a cylindrical and a conical refining gap in series can be achieved either on one rotor or using two different rotors positioned one behind the other. In both cases, the sequence of the series is arbitrary and depends only on the pulp characteristics to be obtained.
A favorable further development of the invention is characterized by internals, particularly paddles, being mounted in the pulp feed channel and/or inlet pipe. Internals of this kind in the inlet pipe or the pulp feed channel can significantly increase acceleration of the liquid even further in addition to the effects of wall friction.